Inkjet recording is widely used as a printing method for offices and homes as digitalization of information progresses. In recent years, a large number of applications such as commercial printing and printing on textile have been developed. As applications of inkjet recording are widely developed, as a coloring agent used in an inkjet ink, not only a conventional water-soluble dye such as an acid dye or a direct dye, but also a water-insoluble coloring agent is used according to the application; in other words, various coloring agents such as a disperse dye and a pigment are used.
In general, it is known that a recording image using a water-soluble dye as a coloring agent has low durability to light, ozone, water and the like.
On the other hand, it is known that a recording image using a pigment as a coloring agent is excellent in various types of toughness to light, ozone, water and the like.
However, when an ink containing a water-insoluble coloring agent such as a pigment loses water due to a certain factor and is thereby brought into a dried state, the dispersed state of the pigment is destroyed, with the result that the pigment is disadvantageously aggregated. It is impossible to return the once aggregated pigment in the ink as described above to the dispersed state even by the addition of a liquid medium such as water (since its redispersibility is poor), and thus an improvement is highly required.
In particular, it is required for an ink containing a pigment to be stable for a long period of time. It is known that a pigment whose particles are present in a dispersed state in an ink undergoes a sedimentation phenomenon caused by the aggregation of the pigment particles over time. Hence, disadvantageously, for example, a concentration gradient is produced in the ink and it is impossible to obtain the initial printing characteristics. Furthermore, the aggregated particles clog in a nozzle, and thus it is impossible to discharge the ink, with the result that improvement is highly required to help solve such problems.
As an inkjet ink using a pigment, there is an ink disclosed in Patent Document 1. This is a dispersed ink composition using a polymer dispersing agent. Patent Document 2 discloses an ink composition using a self-dispersed pigment.
In recent years, a method of mixing a resin into an ink to perform curing and fixing with thermal processing on a record-receiving material has also been known, for example, that disclosed in Patent Documents 3 and 4.
Patent Document 1: Japanese Patent No. 3534395
Patent Document 2: Japanese Patent No. 4016483
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2011-246633
Patent Document 4: Japanese Unexamined Patent Application, Publication No. H09-143407